The HTB hysteresis mode reduce the CPU load, but at the
cost of scheduling accuracy.

On ADSL links (512 kbit/s upstream), this inaccuracy introduce
significant jitter, enought to disturbe VoIP.  For details see my
masters thesis (http://www.adsl-optimizer.dk/thesis/), chapter 7,
section 7.3.1, pp 69-70.
Signed-off-by: NJesper Dangaard Brouer <hawk@comx.dk>
Acked-by: NMartin Devera <devik@cdi.cz>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>